The present invention relates generally to compositions for the oral administration of proteinaceous materials in biologically active form and methods and apparatus of making same. More particularly, the present invention relates to compositions for the treatment of diabetes by oral administration of insulin.
Many drugs, medicaments, and therapies are administered parenterally because they are degraded or not adequately absorbed in the stomach and gastrointestinal tract and therefore cannot be administered orally. For example, as discussed in detail below, insulin is administered through subcutaneous shots to many patients suffering from diabetes mellitus.
Diabetes mellitus is a chronic disorder affecting carbohydrate fat and protein metabolism. It is characterized by hyperglycemia and glycosurea resulting from a defective or deficient insulin secretory response. Two major variants of the disease exist. The number of patients diagnosed as diabetic is estimated to be 10 million in the United States alone and this figure is believed to be increasing at a rate of 6% per year.
One variant, seen in about ten percent of all idiopathic diabetics, is referred to as insulin-dependent diabetes mellitus ("IDDM") or juvenile onset diabetes. This variant is frequently manifested for the first time in youth and is characterized by a progressive loss of insulin secretory function by beta cells of the pancreas and hence a pregressive "dependency" on exogenous insulin for maintenance of carbohydrate metabolism. (This characteristic is shared by those non-idiopathic, or "secondary", diabetics whose disorders have their origins in pancreatic disease.) The second variant of idiopathic diabetes mellitus is referred to as non-insulin-dependent diabetes mellitus ("NIDDM") or adult onset diabetes mellitus and accounts for the remainder of the idiopathic diabetic population.
All diabetics, regardless of their genetic and environmental backgrounds or the age of onset of the disease, have in common an apparent lack of insulin or inadequate insulin function. Because transfer of glucose from the blood to the muscle and fatty is insulin dependent, diabetics lack the ability to utilize glucose adequately. Further, because glycogenolysis is ordinarily inhibited by insulin, the rate of glycogenolysis is elevated in the diabetic. Both these "derangements" from normal metabolic events lead to accumulation of glucose in the blood (hyperglycemia) to the point where renal glucose reabsorption capacity is exceeded and glycosuria occurs. The major source of energy for the diabetic thus becomes fatty acids derived from triglycerides stored in fatty tissue.
In the liver, fatty acids are oxidized to ketone bodies which are circulated and used as an energy source by tissues. In the IDDM patient, and sometimes the NIDDM patient, the rate of formation of the ketone bodies may exceed their rate of their utilization and ketosis along with metabolic acidosis may occur. Since tissues appear to be starving for glucose, dietary and tissue sources of protein are used in glucogenesis. Anabolic processes such as synthesis of glycogen, triglycerides and proteins are "sacrificed" to catabolic activities including glycogenolysis, gluconeogenesis and mobilization of fats. Thus, the diabetic state which has its origins as a "simple" insulin defect, results in widespread metabolic disturbances having long-term pathological effects on nearly all organs and tissues of the body. Indeed, the diabetic state is one of the prime contributors to deaths caused by myocardial infarction, renal failure, cerebrovascular disease, atherosclerotic heart disease, and systemic infections.
The hyperglycemic and glycosuric conditions of the diabetic disease may be remedied by a manipulation of the diet, control of body weight, and regulation of physical activity. In some diabetics, particularly those suffering from NIDDM, the hyperglycemic and glycosuric conditions can be managed by oral administration of anti-hyperglycemic agents such as derivatives of sulfonylureas, sulfonamides, biguanides and other compounds. For diabetics suffering from IDDM and advanced NIDDM, however, therapy has focused on administration of exogenous insulin.
Insulin is a polypeptide produced in the islets of Langerhans located in the pancreas. The insulin molecule is initially sythesized as a single polypeptide chain but is processed such that in its active form it consists of two amino acid chains joined by two cysteine disulfide bonds. One of the two chains is folded back upon itself as a result of a third disulfide bond. The entire molecule has a molecular weight of 5,734 and is dependent upon the disulfide bonds to maintain its biologically active conformation.
While in the past, exogenous insulin has been derived primarily from bovine and porcine sources it has recently been obtained in "human" form as a result of recombinant DNA technology. The availability of "human" insulin derived from recombinant sources has proven to be greatly beneficial to those diabetics with an intolerance to insulin derived from animal sources.
Nevertheless, the greatest problem with respect to insulin therapy is not related to the source of the insulin but rather to its method of introduction to the body. The most common method for the administration of insulin is that of subcutaneous injection. This method is inconvenient, painful, and may itself exacerbate the pathology of the disease. Subcutaneous injection of insulin gives rise to relatively high insulin levels in peripheral tissues and relatively low levels circulating through the liver, the primary site of endogenous insulin activity. High levels of insulin in peripheral tissue have been associated with blood vessel pathology (e.g., blood vessel constriction and permeability changes) and pathologic effect on associated peripheral tissues, e.g., diabetic retinopathy. The "swamping" effects of subcutaneously administered insulin on peripheral circulatory tissues eventually reduces the amount of insulin circulating to the liver--again resulting in the need for increased doses to achieve desired metabolic effects. For these various reasons an alternative to injection as a method for the administration of insulin has long been sought.
As an alternative to the injection of insulin, some workers have directed their effort toward the intra-rectal administration of insulin by means of suppository. U.S. Pat. No. 2,373,625 issued to Brahn, discloses insulin suppositories containing weak organic acids such as lactic acid or citric acid in combination with a surfactant.
Also known in the art are insulin suppositories utilizing a variety of ingredients such as saponin, corn oil, polyoxyethylene-9-lauryl-alcohol and polyoxyethylenelaurylether. Insulin has also been encapsulated into acrylic acid-base water soluble gels and into soft gel capsules containing surfactants. Although the method of intra-rectal administration of insulin shows promise the results of bioavailability tests have been inconsistent and the method is inconvenient.
Ishida, et al., Chem. Pharm. Bull., 29, 810 discloses a method whereby insulin may be administered via the buccal mucosa of the mouth. Insulin was mixed with a cocoa fat base and a surfactant before administration to the buccal mucosa. Experiments in dogs demonstrates only poor bioavailability of insulin so administered.
Other workers have directed their efforts towards intrapulmonic administration of insulin. Wigley, et al., Diabetes, 20, 552 (1971) discloses administration by means of a nebulizer of insulin at 500 U/ml in particles 2 m in diameter. A hypoglycemic response was observed after 30 U/kg of body weight which indicated a total bioavailability of roughly 7 to 16%. Yoshida, et al., J. Pharm. Sci. 68, 670 (1979) discloses an intra-pulmonic introduction of insulin combined with lactose and acethylglycerinemonstearate, dissolved in fluoroethane. The aerosol induced hypoglycemic response when administered at an amount 2.5 U/Kg of body weight to rabbits.
Another method of administering insulin that has demonstrated promise is the intra-nasal administration of insulin. Hirai, et al., Int. J. Pharm., 9, 165 (1981) discloses the intra-nasal administration of insulin in combination with a surfactant such as sodium glycocholate solution. Nagai, et al., Journal of Controlled Release, 1, 15 (1984) discloses high bioavailability of insulin when administered intra-nasally to dogs. In this method, crystalline insulin was dissolved into a 0.1 N HCl solution to which a surfactant was added. The solution was then adjusted to a pH of 7.4 by addition of a 0.01 N NaHCl solution and freeze dried. The solution was then mixed with crystalline cellulose prior to its nasal administration.
In the search for alternative methodologies for the administration of insulin it is the oral administration of insulin that has received the most attention. A methodology for the oral administration of insulin would be highly desirable for reasons of safety, convenience, and comfort and would avoid many of the shortcomings suffered by methods involving injection of insulin. Despite the apparent desirability of methods for oral delivery of insulin two major difficulties have limited the success of attempts to fashion oral insulin therapeutics.
The first major difficulty in fashioning oral insulin therapeutics is that the insulin polypeptide is inactivated in the gastrointestinal tract by enzymes such as trypsin, chymotrypsin and other lytic enzymes. The insulin polypeptide is a relatively simple one and with its two disulfide bonds is easily degraded under the harsh conditions of the stomach and gastrointestinal tract.
The second difficulty with the oral administration of insulin is that even if the polypeptide evades degradation in the stomach and gastrointestinal tract it is poorly, and inconsistently, absorbed through the gastrointestinal membrane. Because of its poor bioavailability large oral doses must be given to ensure a hypoglycemic effect. Because inconsistent amounts of insulin are made available, the advantages of an oral administration method may be outweighed by the fact that under-or overdoses of insulin can be more of a health hazard than no insulin at all.
Several approaches have been followed in attempting to overcome the inherent difficulties of oral insulin administration. Some of these approaches include attempts to either inactivate the lytic gastrointestinal enzymes responsible for inactivation of the insulin function or to provide insulin analogues resistant to inactivation by such enzymes. Sichiri, et al., To-Nyo-Byo (Japanese Diabetes Publication), 18:619, 1975, discloses an insulin analogue (beta-Naphthyl-azo-Polystearryle-insulin) which when administered orally to rabbits at 150 IU/Kg body weight induced a hypoglycemic response. Other workers have attempted to make alkyl compounds of insulin by adding triethylamine HCl as well as a surfactant. Teng, oral presentation at the American Diabetic Society Meeting, May, 1983, San Antonio, Tex.
Attempts to prevent insulin degradation by inactivation of lytic enzymes in the gastrointestinal tract have met with some success. Danforth, et al., Endocrinology, 65, 118 (1959) discloses an insulin composition administered orally with isopropylfruorophosphate (an inhibitor of trypsin and chymotrypsin) and indole-3-acetate (an inhibitor of the enzymes known as "insulinase" found in the liver). The composition was found to induce a hypoglycemic effect when administered orally to rats. Other workers have disclosed mild (equivalent to 3% bioavailability of insulin) hypoglycemic responses after the oral administration of insulin along with pancreas inactivating agents (Laskowski, et al., Science, 127, 1115 (1958)). Other workers have found that the oral administration of insulin results in low bioactivities as a result of insulin inactivation in the stomach by pepsin and because of poor absorption through the intestinal membrane (Crane, et al., Diabetes, 17, 625 (1968)).
Workers have also attempted to increase the bioavailability of orally administered insulin by administering the insulin with surfactant agents. The use of surfactant agents such as polyethylene glycol-1000 monoacetyl ether and sodium lauryl sulfate with triethylamine HCl have demonstrated the ability to increase insulin bioavailability to some degree; although 35 units of insulin administered orally had an effect on the blood sugar level equivalent to that of only 4 units administered intravenously (Touitou, et al., J. Pharm. Pharmacol., 32, 108 (1980)).
Efforts have also been directed toward the oral administration of insulin in conjunction with an emulsion system. One group of investigators (Sichiri, et al., Acta Diabet. Lat., 15, 175 (1978)) disclose that they observed a hypoglycemic effect upon administering a water/oil/water emulsion system with added insulin to rats. A 250 IU/Kg of body weight dose was reported to produce an effect equivalent to a 10 IU/Kg dose administered intramuscularly. Insulin has also been administered by means of other emulsion systems utilizing fat soluble vitamins although the hypoglycemic effects in animals such as dogs have been mild and not dose responsive.
Some of the most promising efforts towards increasing the bioavailability of orally administered insulin lie in efforts to microencapsulate insulin materials. Insulin has been microencapsulated in acrylic acid esters (Sichiri, et al., Acta. Diabet. Lat., 15, 175 (1978)) and the use of high molecular polymers has also been disclosed. Other workers have microencapsulated insulin in liposomes of various lipid compositions. Insulin containing liposomes have been formed with compositions such as phosphotidyl choline, cholesterol and stearylamine; dimyristoyl phosphatidylcholine; dimyristoyl phosphatidylcholine and cholesterol as well as with lecithin and cholesterol and other materials.
Dobre, et al., Rev. Roumanian Med.-Encdocrinol 22, 253 (1984) discloses methods of entrapping insulin into liposomes for oral administration. Various materials for the construction of liposomes are disclosed including: egg yolk phosphatidyl choline, cholesterol, stearylamine, and dipalmitoylphosphatidyl choline. Even liposome coatings, however, fail to completely protect the enclosed insulin from the degradation effects of hydrochloric acid found in the stomach and enzymes such as pepsin, trypsin and chymotrypsin found in the gastrointestinal tract.
Yoshida, et al., EPA 140,085 discloses insulin containing lipid vesicle preparations comprising lipid vesicles which are composed of an inner aqueous phase in the form of an aqueous solution or suspension of phospholipid.